Al-Bitruji

Al-Bitruji, known in Latin as Alpetragius, was an Andalusian astronomer and philosopher born around 1150 CE in Pedroche, in the region of Cordoba, Spain. He grew up in the rich intellectual environment of Islamic Iberia, where Greek, Arabic, and Jewish scholarship converged. His formative years were spent under the influence of the great philosopher Ibn Tufayl, and later Ibn Rushd (Averroes), whose circle he joined in Moorish Spain.

Al-Bitruji became deeply dissatisfied with the Ptolemaic model of planetary motion, which required the use of epicycles, equants, and eccentric circles — mathematical devices he considered physically implausible and philosophically incoherent. Drawing on Aristotelian physics and homocentric sphere models pioneered by the ancient Greek Eudoxus, he proposed an entirely new system of celestial mechanics in his landmark work Kitab fi'l-Hay'a (Book on Astronomy). In this system, all heavenly bodies moved in perfect circles around the Earth, driven by a single prime mover whose motion cascaded downward from the outermost sphere.

Though his model was ultimately less accurate in predicting planetary positions than Ptolemy's system, it was enormously influential in medieval Europe. Translated into Latin in 1217 CE by Michael Scot, his Kitab fi'l-Hay'a became a standard reference in European universities, shaping astronomical debate for centuries. His work was cited by Roger Bacon, Albertus Magnus, and later Copernicus, who acknowledged the inadequacy of Ptolemaic epicycles before proposing his heliocentric alternative. Al-Bitruji died around 1204 CE in Morocco, leaving behind a legacy as one of the boldest critics of received astronomical wisdom in medieval science.